Field of the Invention
The invention relates to a rectifier circuit in a three-phase bridge connection with four-segment switches as main switches.
The proposed rectifier circuit can be used, for example, in electric drive engineering (DC drives), in battery chargers and in uninterruptable power supply systems.
Since DC drives can be operated in four quadrants (DC voltage greater than, equal to or less than zero, direct current greater than, equal to or less than zero) reversible converters, i.e. two antiparallel six-pulse groups (rectifiers, power converters) with a total of twelve thyristors are generally used for feeding them when conventional technology is used. In that case, at the change-over from the motive mode to the generating mode, and conversely from the generating mode into the motive mode, either disadvantageous dead times have to be accepted or additional circuit current inductors for the circuit currents which flow have to be installed and special driving methods have to be implemented. The functional principle of such converters requires that reversible converters draw non-sinusoidal currents from the three-phase network and that they cause considerable harmonics, reactive power and network reactions, so that there is the disadvantageous need to provide costly filters in the three-phase network.
If a sinusoidal, three-phase current flow is required in the medium power range, an IGBT converter, including a network-side PWM rectifier (pulse-width-modulated rectifier) and a four-quadrant converter, can be used. The PWM modulation method enables sinusoidal network currents with an adjustable power factor to be implemented. Ten IGBTs with ten inverse diodes are required, together with expensive and comparatively unreliable electrolyte capacitors in the intermediate circuit. The considerable switching losses due to the hard switching processes limit the maximum switching frequency of such converters in the medium power range to 10 to 20 kHz with an efficiency rate of approximately 90%.